Getting stuck behind a service vehicle like a fire truck, school bus, or ambulance can give you time to think. (If it’s a school bus, it can also give you time to make faces at the children, or ponder the loss of innocence as a 9-year-old gives you the finger.) If you have a car that sits low enough to the ground, you might be able to catch a glimpse of chains hanging from underneath the truck. Why are they there?

Unlike many of life’s disappointing explanations for mysteries, the reason behind them is actually pretty neat.